Information from the accident scene may be transient and time sensitive evidence such as: tire marks, gouge marks, debris, paint or other markings from law enforcement investigations, fluid stains, blood spots, disturbed soil or vegetation, and roadway conditions. Over time, some of this transient evidence will fade or disappear completely.

Other important information from the scene pertains to site geometry. This data is usually more permanent and may include: number of traffic lanes and lane widths, lane orientations, compass headings, gradient, slope, super elevation, surface materials, traffic control devices, significant landmarks, sightlines, sight obstructions, ambient and artificial lighting sources. The documentation of these geometric features is utilized for creating scene diagrams, computer simulations, and computer animations. Scene geometry also plays a significant role in performing many traffic collision reconstruction calculations and in considering human factors contributing to traffic accident causation.

Oftentimes, when a forensic expert witness is first contacted for a case assignment there has already been a degradation or loss of physical evidence. Therefore, it is important for those involved early on in a case (whether an attorney, insurance company, or involved party) to take action to preserve vehicle and scene evidence and/or have an appropriate forensic expert witness perform inspections as soon as possible after the accident or collision event.